Lipid Droplet metabolism dependent microbial defense in pre-immune zebrafish embryos

Microbes present survival challenge to pre-immune embryos. Our study provides evidence for antimicrobial-secretion-based strategy of zebrafish embryos against microbes during pre-immune stages. Chorion prevents physical contact between embryos and microbes, yet microbes compromise embryonic survival through their secretions. Development of embryos in microbe-free medium involves secretion of pro-microbial compounds that bacteria utilize to accelarete growth. Embryo senses presence of microbes through microbial secretions. They respond by altering their secretions to include antimicrobial compounds along with regular pro-microbial ones. Upon sensing embryonic anti-microbial secretions, microbes too alter their secretions to include more potent toxins for embryos. In response to this embryos alter their secretions to include more potent antimicrobial compounds. Ability of embryos to secrete antimicrobial compounds is positively correlated with amount of lipid droplets (LDs) in them. Inhibition of LD metabolism prevents antimicrobial secretions by embryos. Thus, LDs protect zebrafish embryos from microbes. This manuscript establishes that pre-immune embryos employ dynamically evolving biochemical warfare to protect themselves from harmful microbes.